1. Field of the Invention
The present invention relates to a linear light source apparatus and an image reading device including the linear light source apparatus.
2. Description of Related Art
An image reading device for reading documents is incorporated in, for example, a facsimile machine, a copier, and a scanner device. FIG. 20 shows an example of such an image reading device (for example, see JP 2007-27137A). The image reading device X shown in FIG. 20 includes a linear light source device 90, a lens array 94, a light-receiving element 95, a substrate 96, a case 97, and a glass cover 98 for loading a document G. The image reading device X reads the document G by illuminating the document G with the linear light source device 90 and guiding the light reflected from the document G through the lens array 94 to the light-receiving element 95.
FIG. 21 is a perspective view of the linear light source device 90. As shown in FIG. 21, the linear light source device 90 includes a white cover 91 elongated in the x-direction, an LED unit 92 assembled at one end of the white cover 91 in the x-direction, and a light-guiding member 93 that is formed in the shape of an elongated rod elongated in the x-direction and is housed in the white cover 91. The light-guiding member 93 includes a light exit portion 931 exposed from the white cover 91, a light-reflecting portion 932 for reflecting light to the light exit portion 931, and a pair of end faces 933 and 934 standing perpendicularly to the light-reflecting portion 932 (see FIG. 20). The pair of end faces 933 and 934 constitute surfaces that are parallel to each other and spaced away from each other in the y-direction. The light emitted from the LED unit 92 in the x-direction enters the light-guiding member 93 and travels inside the light-guiding member 93 in the x-direction, while being reflected. Any component of the light traveling inside the light-guiding member 93 that is reflected in the z-direction by the light-reflecting portion 932 is emitted in the z-direction from the light exit portion 931.
In the image reading device X, a document may be placed on the glass cover 98, with part of the document being suspended in the air. To appropriately illuminate such a suspended part of the document, the irradiation area of the linear light source device 90 needs to be extended in the y′-direction. On the other hand, extending the irradiation area of the linear light source device 90 in the y′-direction poses a problem in that the illuminance per unit area decreases, and it is desired to efficiently emit the light from the LED unit 92 in an emitting direction L.
However, the pair of end faces 933 and 934 of the light-guiding member 93 are parallel to each other, and therefore the light that is incident normally on one of the end faces 933 and 934 is reflected so as to be directly incident normally on the other of the end faces 933 and 934. Such light keeps being reflected inside the light-guiding member 93 without proceeding to either of the light exit portion 931 or the light-reflecting portion 932, and thus will not be emitted from the light exit portion 931 to the outside of the light-guiding member 93. In order to increase the quantity of light from the linear light source device 90, there is demand for an innovation for achieving a further reduction of such light that is not emitted to the outside.
Further, the image reading device X has another problem in that part of the light emitted from the linear light source device 90 is blocked by the lens array 94, resulting in a reduction in the quantity of light reaching the document G.